Radioreceiver control



July 5, 1932- w. H. GRIMDITCH AL RADIORECEIVER CONTROL Filed July 24,1928 2 Sheets-Sheet y 5, 1932- w. H. GRIMDITCH ET AL 1,866,462

RADIORECEIVER CONTROL Filed July 24, 1928 2 Sheets-Sheet 2 jv az/ezazr95g Patented July 5, 1932 uNrre STATES PATENT OFFICE WILLIAM H.GRIMDITCH, 01? GLEN SIDE,

AND DAVID P. EARNSHAW, OF PHILADELPHIA,

PENNSYLVANIA, ASSIGNORS TU PHILADELPHIA STORAGE BATTERY COMPANY, OF GPHILADELPHIA, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA RADIORECEIVERCONTROL Application filed July 24, 1928. Serial No. 295,055.

This invention relates to improvements in devices for controlling theoutput signal volume of electrical signalling systems such as used forexample in radio receiving apparatus, and relates more particularly toimprovements in devices for controlling the output volume of suchsystems having multiple stage tuned radio'frequency amplificatlon.

While the invention in its broader aspects is applicable in general tosignalling systems having a plurality of tuned circuits employingunilateral mutual impedances, such as vacuum tubes, as the couplingelements, it has a particularly useful application in radio receivershaving tuned cascaded vacuum tube amplification with a single" tuningcontrol for all stages and in which also an auxiliary tuning device isused to bring the antenna coupling stage to resonance. V I

The principal object of this invention then is to provide novel andimproved meansfor controlling the output signal volume of radioreceivers of the general character set forth above.

In the attached drawings Figure 1 shows a typical radio receiving systemto which the invent-ion is applicable and illustrates one embodiment-ofour invention; i

Figs. 2 and 3 are enlargedviews illustrating the mechanical details ofthe apparatus, and r Figs. 4:, 5, 6 and 7 are diagrams illustratingseveral alternative dispositions ofcircuit elements with which thisinvention is applicable. 7 r

The methods-heretofore employed for controlling the output volume ofradio receiving apparatus are generally undesirable for use in receiversemploying vacuumtubes whose filaments are energized by alternatingcurrent, Practical results have been obtained, however, by means of aresistor system associated with the antenna circuit in conjunction withan auxiliary tuning device capable of compensating for any detuningeffects caused by the use of antennas and antenna circuit elements ofvarying capacities} This method of control, however, while generallysatisfactory has been found to possess an inherent'defect,

in that the output signal of the receiver, when tuned to a powerfulstation at a moderate distance, is of such high intensity that asatisfactory minimum of signal strength may be unobtainable in spite ofthe fact that the primary of the first radio frequency transformer maybe practically short-circuited' at the minimum setting of the volumecontrol.

lVe have discovered satisfactory and inexpensive means for controllingthe volume whereby the signal intensity may be reduced to a desiredminimum Without adversely affecting the action of the receiver, andwhereby also a beneficial increase in apparent lectivity may be secured.

With reference to the drawings, Figure 1 shows a wiring diagram of thetuned radio frequency system of a radio receiver in which the variousmain tuning elements are actuated from a single or common control andin"? which the vacuum tube cathodes are energized by low potentialalternating current. The main tuning means consists of a plurality ofcondensersl associated respectively with the grid or input circuits ofthe various tubes," and these condensers as indicated in broken linesare operatively connected so as to be adapted for simultaneous operationfrom a ingle control element. Means is also provided for bringing theantenna circuit into plate bypass condensers' l, plate circuit resistors5, and filament bypass condensers 6 being. mcluded for a s1milarpurpose, and to reduce any extraneous disturbrances occurring 1n thispart of the c1rcu1t.

The bilateral mutual impedance system including condensers 3 and theportion 7 of the transformer secondary windingbetween -the indicated tapand the ground is adjusted to balance the bilateral mutual impedancesystem including the interelectrode capacity 8 of the vacuum tube andthe primary 9 of the transformer. These systems form a ba ancedelectrical bridge and allow the vac-- uum tube to perform its functionas a unilateral mutual impedance device, without disturbance due toenergy present in the secondary 10 of the transformer. Condensers 11 areadded to equalize any irregularities of the circuit capacities whichmight otherwise antenna and with the primaryof the first or input radiofrequency transformer in the manner illustrated. In so far as describedabove, the. system. illustrated in- Fig. 1 of the drawings presents nonovelty over prior practice relating to radio receiving apparatus ofthis general character, and: no detailed, desoription of thesystem as awhole is necessary.

In; the illustrated embodiment of the invention, we associate a switch14 with the auxiliary tuning condenser 2 in; such manner that in certainpositions of adjustment of the auxiliary tuning condenser the grid ofthe first radio frequency amplifying tube is disconnected from. itsnor-mat circuits in the man ner shown and is connected to thegrounded'or zero-potential side of the circuit while in other positionsofthis condenser, the aforesaid grid is connected in its normal circuitwith the result that the auxiliary tuning device functions in a normalmanner to. bring its associated tuning circuit into. close resonance.The switch 14 when in-the first-mentioned position and asshown in. Fig.1, operates to ground the grid of the first radio frequency amplifyingtube, thus rendering the tube ineffective as an amplifier whilemaintaining; the normal average energization and the directcurrentinterelectrode potentials substantially the same, and unbalancing theabove-mentioned neutralizing system.

The-tuned secondary circuit of the first radio frequency transformer isnow connected through the neutralizing condenser 3 to. portion 7 of thegridcircuit of the next radio frequency amplifying tube, to whichportion a current can flow by reason ofsaid unbalancing, therebyreducing the-radio frequency amplification; and, therefore, the outputvolume. to, aidesired-extent, andallowing the regular volume control 13to-control the-volume of the reducedsignal in the'normal manner. It"will'be apparent, therefore, that the device provid'estwo distinctranges of operation, in

eachiof. which the volume control 13- is opera- "I,

tirev toregulate the volume as required. In

one of these ranges, the output signals range from a desired minimum toa moderate intensity, while in the other range the signal volume variesbetween a moderate intensity and maximum volume. Also, in the lower in-.T

tensity range, the relative number of tuned circuits is increased inproportion to the number of amplifying tubes, as compared with the highintensity range, thereby obtaining a substantial increase in relativeselectivity in accordance with well known principles.

In Figs. 2 and 3, we have illustrated one form of mechanical means bywhich our invention may be practiced. In this instance, we provide aswitch consisting of contact members 15 and 16 anda blade 17 whichnormally isheld' out of contact with the member 15; and in contact. withthe member 16' by means ofa spring 18. The blade 17 projects into thepath of a contact flange 19 on the rotor 20' of the condenser 2 and isprovided at its, outer end with a shoe 21 which may be; ofiinsulating orconducting material and is. so formed that. when said. flange comes incontact therewith, the b1ade17 iselevated into contact with the member15 and is withdrawn from. the contact 16. It will be noted,- wever, thatthe. flange functions to: close the circuit.15.-17 and open the circuit1617 through; an angular movement of the rotor of approximately duringwhich the ca.- pacity of the condenser varies between its minimum andmaximunnthe circuit 16-1-7 being closed and the circuiti151-7 being openduring. the. remainder of the rotative movement, andthatby reversing thedirection of said movement from: theminimum capacity position, the,capacity may be increased to the maximum while the latter condition ofthe circuits prevails. thusmadeefl'ective for both ranges of control.

In F igs- 4,. 5, 6 and 7,. wehave illustrated circuits similar to -thatshown in Fig. 1, but differing from the latter in the method ofauxiliary tuning; control. and other details :1

In each instance, the circuitincludes the device of the presentinvention. In Fig. igthe auxiliary" tuning device takes the form of avar-iometen-22 located: in series with the anteam, which: latterisconnected? through a 151 condenser 23 directly to the volume controlVariable, resistor 24: A. switch 25 is. connected between" the groundand the grid of the; vacuum t-ubewhich latter is also connectedthrougharesistor 26 to the first tuned cirthe, tube. inoperative, andi allowingthe signals to; be transferred to the: succeeding; circuits .by'means ofinterelement-iinduotions and without. amplification. A variation to benoted; is thatthesuppressor resistor 26' connected-.asillustratedservesin the well known The condenser 2 is 1 manner to suppress the tendencyof the tube to generate oscillations. Another variation "is that theresistor 24: is so connected as to vary the proportion of the antennacurrent 'flowing in the first tunedcircuit, thereby regulating thevolume;

In Fig. 5, we have shownthe antenna connected through a tap directly tothe grid tuning coil of the first stage of radio frequencyamplification. In this case, the auxiliary tuning device takes the formof a variable condenser 27, in series with the antenna, and thisauxiliary tuning'control is operatively connected with a switch 28 in amanner similar to that described in connection with Fig. 1

whereby in one part of the rotation of the condenser 27, the switch ismade to disconnect the'grid from the tuned circuit and to connect it toground. The broken line 29,

Fig. 5, serves to illustrate that it is expedient but not necessaryeither in this instance or in the other embodiments herein described toground the grid when it is'discon'nected from the tuned circuit, analternative connection being to a point of any desirable dipositions ofthe variometer, the switch connects the grid to ground. In thisinstance, it will be noted that the switch 33 is connected between thegrid of the tube and a suppressor resistor 34 as an alternative to theconnection in the neutralized type of circuit, as shown in Fig. 1. Fig.6 also serves to illustrate possible paths of capacitive induction 35and 36. by which the signal may be transferred to the second tunedcircuit in the low intensity range position in the absence of aneutraliztuned circuits each includlng a tunlng eleing condenser system.

The device of the invention is applicable also to other types of volumecontrol, one

such application being illustrated in Fig. 7 l in which a variableresistor 37 is placed in series with the antenna and with the primary ofthe input transformer. In this instance, the auxiliary tuning device issimilar to that illustrated in Fig. 1. Another variation to be noted isthat a suppressor resistor 38, con-' nected between the grid and theswitch 39 has been substituted for the neutralizing system of Fig. 1.

The invention is applicable in principle to many forms of electricalsignalling apparatus and is not limited in use to radio re-.

ceivers; nor is the invention limited to the particular radio receivingapparatus and arrangements herein set forth for illustrative Y.

purposes. The invention is applicable, for

example, to receivers employing loop antennae; and although in apparatusof the type illustrated an operative connection between the auxiliarytuning controland the volume range switch will be found desirable, byreason of the resultant reduction in the number of manual controls andan increased simplicity of operation, such operative connection is notessential to the functioning of the switch for the purpose described andthe switch maybe independently controlled. Similarly, the invention maybe applied to receivers employing a multiplicity of independent tuningcontrols. The device may vary widely as to detailed form and as to itsposition in the electrical system with which it may be associated.

We claim: 7

1. In a signalling system, a unilateral mutual impedancedevice, a signalcircuit preceding said device and a signal circuit succeeding saiddevice, an electrical circuit including said unilateral mutual impedancedevice connecting said signal circuits, an'electrical circuitindependent of said device continuously connecting said circuits, andmeans whereby said first-mentioned electrical circuit may be renderedineffective.

2. In a signalling system, a plurality of tuned circuits each includinga tuning element, said elements being controlled by a common means, atuning element auxiliary to one of said tuning elements, a unilateralmutual impedance device interposed between two of said tuned circuits,and adjustable means operatively associated with said auxiliary elementwhereby in one position of said means a portlon of a signal transferredfrom one tuned circuit to a succeeding tuned circuit passes through saidunilateral mutual impedance device, andin another position of said meanssubstantially no portion of the signal passes through said unilateralmutual impedance device.

3. In a signalling system, a plurality -mutual impedance deviceand abilateral mutual impedance system each arranged to transfer energy fromone of said tuned circuits to another of saidcircuits, said bilateralsystem being continuously efi'ective, and

means operatively associated with said auxiliarytuning element forrenderlng said unilateral mutual impedance device efiective orsubstantially ineffective.-

" 1. In a signalling'system, aplurality of signal circuits, aselectively adjustable tuning elementelectrically associated with one ofsaid signal circuits, a unllateral mutual im- =pedancedevice having acontrol electrode connected to one of said slgnalcircuits, and

a switch mechanically associated withsa-id' adjustable element arranged,to disconnect; the saidcontrol electrode from the signal circuit and tosubstantially simultaneously ground the control electrode. 1

5. In a signallingsystem, a plurality of signal circuits, a unilateralmutual impedance device and external thereto a bilateral mutualimpedance system each arranged to transfer energy from one of saidsignal circults to another of said signal circuits, said bilateralsystem being continuously effective, and means for rendering saidunilateral mutual impedance device efiective or substantiallyineffective.

6. In a signalling system, a plurality of signal circuits, a selectivelyadjustable tuning element electrically associated with one of saidsignal circuits, a unilateral mutual impedance device and abilateral'mutual impedance system each arranged to transfer energy fromone of said signal circuits to another of said signal circuits, andmeans mechanically associated with said selectively adjustable tuningelement for rendering said unilateral mutual impedance device effectiveor substantially ineffective.

7. In a signalling system, a plurality of signal circuits, a unilateralmutual impedance device and external thereto a bilateral mutualimpedance system each arranged to transfer energy fromone of said signalcircuits to another of said signal circuits, said bilateral system beingcontlnuously effective and said unilateral mutual impedance devicehaving a control electrode connected to one of said signal circuits, andmeans operative on the control electrode for renderin the unilateralmutual impedance device effective or substantiaily ineffective.

8. In a signalling system, a plurality of,

signal circuits, a unilateral mutual impedance deviceaud externalthereto a bilateral mutual impedance system each arranged to transferenergy from one of said signal circuits to another of said signalcircuits, said bilateral system being continuously effective and saidunilateral mutual impedance device havlng a cathode and an electrodeconnected to one of said signal circuits, and means for renderingineffective said unilateral mutual impedance device while maintainingthe direct current potential between the cathode and said electrodesubstantially the same.

'9. In a signalling system, a plurality of signal circuits, a unilateralmutual impedance 10. In a signalling system, a plurality of signalcircuits, a unilateral mutual impedance device and a plurality ofbilateral mutual impedance systems, said device and each of said systemsbeing arranged to transfer energy from one of said signal circuits toanother of said signal circuits and one of said bilateral systems beingcontinuously effective, and means for rendering ineffective saidunilateral mutual impedance device and one of said bilateral systems.

11. In a signalling system, a plurality of signal circuits, aselectively adjustable tuning element electrically associated with oneof said signal circuits, a unilateral mutual impedance device and aplurality of bilateral mutual impedance systems, said device and each ofsaid systems being arranged to transfer energy from one of said signalcircuits to another of said signal circuits, and means mechanicallyassociated with said selectively adjustable element for renderingineffective said unilateral mutual impedance device and one of saidbilateral systems.

WM. H. GRIMDITGH. DAVID P. EARNSHAW.

device and external thereto a bilateral mutual I impedance system eacharranged to transfer energy from one of said signal circuits to anotherof said signal clrcults, means for connecting the unilateral mutualimpedance devlce to an energizing source, and means for renderingineflective said unilateral mutual impedance device while maintainingthe normal average energization of the unilateral mutual impedancedevice.

